In recent years, not only in personal computers but also in portable terminal apparatuses such as cellular phones, there are increasing opportunities for exchanging various kinds of information such as electronic mails by manually inputting the information.
Unlike a desktop personal computer, in order to carry a portable terminal apparatus, it is necessary to reduce a terminal main body in size. According to the reduction in size, contradictory requests, i.e., a reduction in size of a key input system and securing of fixed operability, have to be balanced. Therefore, in this type of portable terminal apparatus, various techniques for improving operability in key input are desired.
As a technique for improving operability of key input in a conventional portable terminal apparatus, there is proposed a technique that makes it possible to reduce stress in key operation by a user by changing arrangement of keys in a key operation system and setting of display in a key operation unit, for example, when the user changes a way of looking at a display screen, i.e., when the user changes the direction of a portable terminal apparatus to operate the portable terminal apparatus.
For example, according to a technique described in Japanese Patent Laid-Open No. 2002-51124 and Japanese Patent Laid-Open No. 2005-12493, even when a user changes the direction of a portable terminal apparatus to operate the portable terminal apparatus, it is possible to always maintain the direction of the portable terminal apparatus with respect to the user by rotating operation keys according to the change in the direction of the portable terminal apparatus. Therefore, the user does not need to remember key arrays corresponding to the directions of the portable terminal apparatus. Further, in both a case in which the user holds the portable terminal apparatus with the right hand to operate the portable terminal apparatus and a case in which the user holds the portable terminal apparatus with the left hand to operate the portable terminal apparatus, it is possible to maintain fixed operability by reversing the operation keys according to the respective cases.
However, the technique according to the Patent Documents is essentially a technique for maintaining original operability even when a display screen on which information is displayed is changed to various directions or when a holding position of a terminal main body, i.e., operation of the terminal main body by the right hand or the left hand is changed. Therefore, the technique is not a technique for improving operability of key input itself during normal use.
With these conventional portable terminal apparatuses, all users perform operation according to configurations of keys peculiar to the portable terminal apparatuses during normal use. The respective users have to adapt themselves to the portable terminal apparatuses to operate the portable terminal apparatuses. Movable ranges of fingers depending on sizes of hands of the users, positions for holding the terminal apparatuses, and the like, movable ranges of the fingers depending on a difference of the right hand and the left hand for operating the portable terminal apparatuses, and the like are not taken into account. Even if the users feel that the present key layout is inconvenient, basically, the key layout cannot be changed or corrected to improve operability. Therefore, there is a problem in that it is difficult for some users to use the terminal apparatuses.